The isolate perfused rat heart (Langendorff) and isolated rat myocytes will be employed to assess the role of alpha adrenergic receptors in the control of myocardial metabolic processes - in particular glycogenolysis, amino acid transport, and RNA and protein synthesis. The contribution of alpha vs. beta adrenergic receptors in mediating these metabolic effects of catecholamines will be assessed by the use of a variety of agonists (isoproterenol: predominantly beta; epinephrine: mixed; phenylephrine: predominantly alpha) in the presence and absence of specific antagonists (propranolol: beta and phentolamine, phenoxybenzamine or dehydroergotamine: alpha). The role of calcium ion in these processes will also be investigated by altering both extracellular concentration and flux (employing transport inhibitors, e.g., verapamil and accelerators, e.g., the ionophore A23187). We also plan to determine alpha and beta receptor site number (density) in intact myocardium as well as isolated myocytes by the use of high-specific activity radiolabeled catecholamine agonists and/or antagonists.